This invention relates to a cyanoacrylate composition mainly composed of 2-cyanoacrylate. According to this invention, there are provided compositions which can be used as adhesives having rapid setting time, excellent workability and good storage stability for adhesion of various hard-to-bond porous material such as woods, papers, leather, etc., compositions for molding materials reinforced by mixing with glass fibers, polyethylene fibers, etc. and furthermore, compositions useful for detection of fingerprints.
Adhesives comprising cyanoacrylate compositions have been widely used as instantaneous adhesives in industrial fields, medical fields, leisure fields and in general household use because of their property that they readily undergo anionic polymerization due to adsorbed water on the surface of the materials to be bonded, are rapidly cured and their characteristics that they have low viscosity and are free-flowing one-pack type solventless adhesives.
The compositions of this invention can be similarly used as adhesives in these fields. The fields for application thereof are further extended because of rapid curability, workability and stability in bonding of porous materials. In addition, the compositions of this invention may also be used for shaping materials and for detection of fingerprints.
The following two methods have been mainly employed to prevent absorption of adhesives into porous materials when porous materials such as woods, papers, leathers, etc. which are difficult to bond are to be bonded with cyanoacrylate adhesives or to prevent sagging of the adhesives when microgaps are bonded by penetration bonding.
According to one of them, one surface of material to be bonded is pretreated with a primer containing amines which are curing agents and then treated with a cyanoacrylate adhesive, or curing accelerators are previously mixed in the cyanoacrylate adhesive. As the curing accelerators, there are known complexes of imidazoles and SO.sub.2 (U.S.Pat. No. 3993678), caffeine, theobromine (U.S. Pat. No. 4042442), polyalkylene oxide and its esters or ethers (Japanese Patent Examined Publication No.37836/85) corresponding to U.S. Pat. No. 4,170,585, crown ethers (Japanese Patent Examined Publication No.2238/80) corresponding to U.S. Pat. No. 4,171,416, podant compounds (U.S. Pat. No. 4386193), normal or acid salts of amines or imines (Japanese Patent Unexamined Publication No.141827/79), alcohols, alcohol ester derivative compounds (Japanese Patent Unexamined Publication No.12166/80), polyethylene glycol dimethacrylic esters (Japanese Patent Unexamined Publication No.200469/82), SO.sub.3 complexes of tertiary amines, sulfonium tetrafluoroborate (Japanese Patent Unexamined Publication No.87170/83), polyethylene/propylene oxide monoacrylate, etc. (Japanese Patent Examined Publication No.26513/85), compounds obtained by the reaction of siloxane, phosphoric acid, dicarboxylic acids or their acid chloride, acid anhydride, etc. with diols (Japanese Patent Unexamined Publication No.90277/85), calixarene (Japanese Patent Unexamined Publication No.179482/85), etc.
According to another method, the adhesives are made highly viscous using thickening agents such as polymethyl methacrylate, acrylic rubbers and the like to inhibit absorption of the adhesives into the porous materials. Adhesives of high viscosity which have thixotropic properties are preferred and so, thickening agents which impart thixotropic properties have also been studied and use of fumed silica has been proposed (U.S. Pat. No. 4477607).
When porous materials such as woods, papers, leathers, etc. are bonded by the above two methods, there are the following problems, which hinder further extension of scope of application of cyanoacrylate adhesives.
When curing agents are used and when they are used as primers, an operation of pretreatment of the surface to be bonded is required and this negates the important characteristic of one-pack curing of cyanoacrylate adhesives. Thus, extension of uses cannot be expected, although the instantaneous bonding ability is maintained. Further, inhibition of absorption of adhesives only with addition of curing agent requires a large amount of curing agent, which damages storage stability of adhesives. On the other hand, when a thickening agent is used in order to inhibit the absorption of adhesives into the porous materials, in many cases, it is used in combination with said curing agent to adjust setting time of the adhesives. In this case, when it is attempted to obtain sufficient viscosity, there often occurs stringing, which considerably damages the workability. Fumed silica has been proposed as a thickening agent which causes less stringing and provides thixotropic properties, but use of fumed silica has the problems of separation of components contained in adhesives and settling of fillers. Further, it is difficult to substantially inhibit the absorption of adhesives into porous materials only by increasing the viscosity using a thickening agent. Besides, there occur other problems such as reduction of coatability and bond performance when viscosity is increased. Setting time can be adjusted by joint use of curing accelerators and by increase or decrease of the amount added, but as explained before, with increase of the amount added, storage stability is appreciably reduced.